This invention relates to Stirling engines and to improved methods of operation whereby catalytic oxidation of a major proportion of the fuel takes place in the external combustor.
The Stirling engine when connected to a rhombic or similar drive mechanism is known to possess very little vibration and this results in quiet operation of the engine. Since the fuel is burnt in an external combustor, the exhaust gases are cleaner than a normal diesel or petrol engine.
An object of the present invention is to provide a Stirling engine in which the external combustion unit is a catalytic combustor, such that the engine may be used in conditions where there are limits on noise, pollutants, in exhaust gases and flamable substances.
According to one aspect of the present invention there is provided an external combustion unit of a Stirling engine the unit comprising a catalytic combustor having a thermally stable and oxidation resistant monolith made from and/or carrying a catalytic material and including a multiplicity of flow paths for catalytic combustion of combustible gases and injected fuel.
Using catalytic combustion in the external combustion unit according to the invention enables the engine to be used in areas such as mines and under-water where conventional flame combustion is impractical or is controlled by stringent regulations.
According to another aspect of the present invention, the external combustion unit of the Stirling engine comprises:
(a) a fan for producing a supply of air to the combustor; PA1 (b) a pilot burner fuelled by a fuel injector; PA1 (c) at least one injector for injecting the remaining fuel into the gaseous stream; PA1 (d) a catalytic combustor section comprising a temperature stable oxidation resistant monolith, the monolith providing catalytic channels for contact with and passage of the gases combined with injected fuel at stage (c) such that catalytic combustion of the uncombusted fuel takes place but in which a low pressure drop is produced, and PA1 (e) means for directing the stream of hot gaseous fluid leaving the catalytic combustor over heater pipes of the Stirling engine.